Direct reading radio navigation system



July 18, 1950 M. J. MINNEMAN 2,515,464

DIRECT READING RADIO NAVIGATION SYSTEM Filed April 26. 1947 5Sheets-Sheet 1 July 18, 1950 M. J. MINNEMAN DIRECT READING RADIONAVIGATION sYsIEN 5 Sheets-Sheet 2 Filed April 26, 1947 illllllllL rllllll I |.|l MQSK 25mm WN.

INVENTOR. /l// m/v J/W/A/A/EMAA/ IMI@ ATTORNEY N .WML

5 Sheee'cs-Skxem:A 3-

I/ If@ i ll S-J I I I I M. J. MINNEMAN DIRECT READING RADIO NAVIGATIONSYSTEM k-i--Ismve PER/0p IUAC.

July is, 195o fue@ pi-i1 26, 1947 I mi WIM H m ,Q m w H H m M M I m JAIlll .I mw Aw W HHH .I w w n.. ImIIIIHIIIIImiIIIIIIIIIII I I Ii af M mimIII. 1 Tf/ r HH I I M IIII A. -lIIlII| I.. |I+ -I+ III II w I III n I WY n B HsIII Ll HM/Il IIIV HmI l m I i I I IITIILI .:fJT D EF GHIJ K L MNOPQRSTUM" d ,/a M M M i V\||I %flll. I I I l I l I I I IIIITIIIIIIIIIIIIIIIIIIIIIII. mhd/I ATTORN EY vJuly l'18, 1950 M. J.MINNEMAN 2,515,464

DIREc'l READING RADIO NAvIGA'rIoN SYSTEM Filed April 26. 1947 5Sheets-Sheet 4 July 18, 1950 M. J. MINNEMAN 2,515,464

DIRECT READING RADIO NAVIGATION sYsmA F'ie April 26, 1947 5 sheets-sheet5 rFJy. 6' Jg. 7 jpg. 6

FIXED INDEX MARKER VAR/ABLE INDEX MARKER Jig. 10 FAJrJwEEP Z 2 c/Rcu/r AINVENTOR.

Mmm/v J. M/A//VEMAN ATTORN EY cuits.

Patented Jul/Q 1s, 195o DIRECT READING R ADI() NAVIGATION STEM Milton J.Minneman, Camden, N. J., assignor to Radio Corporation of of DelawareVAmerica, a corporation Application April 26, 1947, Serial No. 744,239

9 Claims. (Cl. 343-103) My invention relates to radio navigation systemsand particularly to systems of the type utilizing the time difference inthe propagation of radio pulses from synchronized ground stations.

Navigation systems of this type employ pairs ofv synchronized groundtransmitting stations that emit radio pulses having a xed time relation.Each pair of ground stations preferably transmits pulses at an assignedindividual repetition rate for the purpose of station selection. Thepulses are broadcast so that they may be received by means of equipmentslocated in the aircrafts or ships whose positions are to be determined.By means" of the receiving equipment, the operator on the craftdetermines the time difference between the pulses from the twotransmitter stations of one pair as they arrive at the receiver. Sincethe radio pulses travel from the'ground transmitters to the receiver ata known propagation rate (i. e., at the velocity of light) it is knownthat the position of the craft is at some point on a line correspondingto the time difference reading. By obtaining the time difference readingfrom a second pairof ground stations, a second line corresponding' tothe second time difference reading is obtained, and the intersect pointof the two lines is the position of the craft. Special maps having thetime difference lines printed thereon for the several pairs of groundstations are provided for use with the navigation system.

In order to measure the time difference in the arrival of successivepulses from a pair of ground stations, the receiving equipment isarranged to generate pulses at selected repetition rates. The pulses maybe adjusted to have a definite time relation to time of arrival of theground station pulses and are provided for the purpose of driving orsynchronizing cathode-ray deecting cir- The deflecting circuits producecathoderay sweep traces on which the received ground station pulses aredisplayed.

For the purpose of selecting a particular pair ofground stations, theoperator selects the particular pulse repetition rate for the driving orsynchronizing pulses corresponding to the repetition period of thepulses transmitted from said pair whereby the deilecting circuits may besynchronized with the received pulses from the selected pair of groundstations, Thus a particular pair of ground stations is selected at thereceiver apparatus by turning a station selection switch to the positionindicated on the receiver panel for obtaining sweep synchronizing pulseshaving the same repetition period as that of the pulses beingtransmitted from the selected pair of ground stations. Now the receivedpulses from the selected pair of ground stations can be made to appearstationary on the cathode-ray sweep Vor trace whereas those receivedfrom the other pairs of ground stations will move along the same trace.

The pulses from the two transmitter stations of a selected pair will bereferred to as A and B pulses, respectively, and the B pulse isidentified in the present system as the pulse that occurs after orfollows the mid-point of the other pulse period. In operation, the A andB pulses are displayed, respectively, first on two slow-sweepcathode-ray traces and then on two fast-sweep cathode-ray traces,thereby enabling the operator to adjust a plurality of delay or phaseshift circuits so that the time dilerence between the pulses driving orsynchronizing the cathode-ray deecting circuits equal exactly the timedifference between A and B pulses.

The adjustment for the display and alignment of the A and B pulses isaccomplished by rst setting the A pulse at the left end of the upperslowsweep trace, when the receiving apparatus is switched to anoperating position marked #1. The B pulse will then appear on the lowercathode-ray trace and a variable index marker may now be located underthe B pulse, this being done by adjusting the several variable delay orphase shift circuits. The apparatus is then switched to a #2 fast-sweepoperation position so that the A and B pulses appear on two fast-sweeptraces, respectively. The starting time of the fast-sweep trace on whichthe B pulse appears coincides with the start of the variable indexmarker, while the starting time of the fast-sweep trace on which the Apulse appears, coincides with theistart of the slow-sweep trace.Therefore, by further adjustment of the delay circuits, the adjustablefast-sweep wave is caused to start at the proper time to bring the A andB pulses into alignment. In order to insure exact alignment, the A and Bpulses should be made to have the same amplitude, and an amplitudebalance control circuit is provided for this purpose. After theseadjustments have been made the time difference between the starts of thefast sweeps will exactly equal the time dierence between the A and Bpulses from the transmitters.

The present invention provides a method and system whereby this timedifference may be determined accurately from the readings of countersthat are mechanically coupled to the several delay or phase shiftcircuits, respectively. The readings of the three counters are inthousands, hundreds, and microsecond units.

It has previously been proposed to determine the time difference of thereceived pulses in navigation systems by Calibrating the delay devicesto obtain a direct reading in microseconds. It was found, however, thatwith the systems then available no precise reading could be obtained inthis way. As a result, timing marks were provided so that they could becounted to determine the time difference within one or two microseconds,for example.

According to the present invention the system is so designed that aprecise time difference reading may be taken directly from the delay orphase shift circuits. The design includes the use of a sine wave phaseshifter that can be calibrated accurately in microseconds, and the useof pulse selecting circuits to which gating pulses are applied under thecontrol oi' calibrated delay circuits, the entire combination havingvarious important features that will be described hereinafter.

An object of the present invention is to provide an improved method ofand means for determining the time difference between electrical ulses.p A further object of the invention is to provide improved receivingequipment for a radio navigation system of the type utilizing thepropagation of radio pulses from pairs of synchronized ground stations.

A still further object of the invention is to provide an improved methodof and means for indicating the time difference between radio pulsestransmitted from synchronized ground stations.

A still further object of the invention is to provide an improved methodof and means for obtaining a direct reading of the time diiferencebetween radio pulses transmitted from synchronized ground stations.

The invention will be better understood from the following descriptiontaken in connection with the accompanying drawing in which Figure 1 is ablock and circuit diagram of navigation receiving apparatus designed inaccordance with one embodiment of the invention,

Figure 2 is a block and circuit diagram of the pulse generating unitshown in Fig. 1,

Figure 3 is ablnck diagram representing one pair of ground radiotransmitter stations of the navigation system which transmit A and Bpulses, respectively.

Figure 4 is a group of graphs which are referred to in explaining theoperation of the system shown in Fig. 1.

Figure 5 is a circuit diagram of a portion of the system shown in Fig.1,

Figure 6 is a view of the slow-sweep cathoderay traces appearing on thescreen end of the cathode-ray indicator tube that is included in theapparatus of Fig. 1 and of the received pulses A and B as they appear onthe traces when they are aligned,

Figure '7 is a view of the fast-sweep cathoderay traces on thecathode-ray tube indicator and of the received pulses A and B as theyappear on the two fast-sweep traces, respectively, during the next stepin obtaining more exact alignment of the A and B pulses,

Figure 8 is a view showing the fast-sweep traces of Fig. 7 superimposedor collapsed for the final alignment step and showing the A and B pulsesexactly aligned and superimposed, and

Figures 9 and 10 are circuit diagrams of the horizontal deflectingslow-sweep and fast-Sweep THE PULSE GENERATOR UNIT In Fig. 1, the pulsegenerating circuit for producing the controlling or synchronizing pulsesthat control the cathode-ray deection is shown in block diagram at thetop of the figure. It is shown in detail in Fig. 2. Referring to Figs. 1and 2, the pulse generator comprises a crystal oscillator I0 thatproduces a sine wave voltage of stable frequency which in the exampleillustrated is 100 kilocycles per second, the repetition period being 10microseconds. The frequency of the crystal oscillator output may beincreased or decreased slightly by a manual adjustment as indicated atthe control knob II for obtaining a tine right or left drift of areceived pulse on a rate of 100 kc. per second. The repetition period ortime interval between successive pulses is, therefore, 10 microseconds.

The frequency of the 10 as. pulses is divided by ilve by means of asuitable frequency divider I3 such as a second blocking oscillator toproduce 50 as. pulses. While specific values are being given fortheseveral frequency division steps, the invention is not limited tothese particular values.

The 50 as. pulsesare applied to a frequency divider I6 of the countertype described in White Patent 2,113,011. It divides the frequency bytwo to produce ps. pulses. .Also. an additional circuit is provided sothat the divider I6 may be made to lose a "count for the purpose ofobtaining a different selected pulse repetition period.

The divider I6 (Fig. 2) comprises a counter circuit portion including aninput or bucket capacitor I1, a pair of diodes I8 and I9, a storagecapacitor 2| and a blocking oscillator portion 22. In addition, itincludes a pair of diodes 23 and 24 associated with the storagecapacitor 2| for the purpose of making the divider I6 lose a count uponthe application of a pulse from a conductor 26 leading from a stationselector switching circuit I4 as will be explained hereinafter. Theblocking oscillator 22 comprises a vacuum tube 21 and a transformer 28coupling the plate circuit to the grid circuit.` The cathode circuitincludes a biasing resistor 29, bypassed by a capacitor 3|, andconnected-in series with a bleeder resistor 29. A transformer 32supplies the 100 ps. pulses from the divider I6 to a frequency divider33 which also is of the type which may be made to lose one or morecounts.

The frequency divider I6 operates as follows: Each of the 50 as. pulsesof positive polarity from the oscillator I3 puts` a predetermined chargeon the comparatively large capacity storage capacitor 2| as a result ofa pulse of current through the comparatively small bucket capacitor |1and through theV diode I9, the capacity of the capacitor l1 being smallenough so that capacitor I1 receives full charge before the terminationof an applied pulse. At the end of this current pulse, the capacitor |1is discharged to ground potential through the diode I8. The next 50,11s. pulse puts an additional current pulse into capacitor 2|, thisraising the voltage across capacitor 2| sulliciently to trigger theblocking oscilator 22 whereby a pulse is produced across the transformer28 as is well understood in the art. The pulse thus produced is appliedto the divider 433 with positive polarity. At the same time, theblocking oscillator 22 discharges thecapacitor 2| to bring it back toground potential.

The frequency divider 33 divides the frequency by iive to produce 500as. pulses. It includes a counter portion comprising a bucket capacitor36, a pair of diodes 31 and 38, and a storage capacitor 39. It alsoincludes a blocking oscillator portion 4| comprising a vacuum tube 42, afeedback transformer 43, a biasing resistor 44 and a bypass capacitor46.

As in the preceding divider I6, there is provided in the divider 33 apair of diodes 41 and 48 for subtracting counts. In the divider 33,however, the application of a pulse from a conductor 49 will subtractone, two, three or four counts depending upon the position of a switcharm 61 which is operated by a knob 65 as well as the right-drift switch96.

The 500 as. pulses are supplied over a conductor 5| to a frequencydivider 52 that divides by two to produce 1000 as. pulses. The divider52 is similar to the divider I6 with the count sub- Y tracting diodesomitted.

The 1000 as. pulses are supplied to a frequencyv divider 5B that dividesby five to produce 5000 as. pulses which, in turn, are supplied to afrequency divider 59 that divides by four to produce 20,000 as. pulses.The dividers 56 and 59 are similar to the divider 52 except for thedifference in circuit constants.

The 20,000 as. pulses may be passed through a clipping circuit 60 andsupplied over a conductor 6| to a square wave generator 65 (Fig. l),such as an Eccles-Jordan oscillator, for obtaining a square wave C (Fig.4) having a repetition period of 40,000 as. This square Wave is thenpassed through a cathode follower tube |5 and from it are obtained, bymeans of suitable wave shaping and delay circuits described hereinafter,the desired driving or synchronizing pulses for the horizontalfast-sweep deflection.

The 20,000 as. pulses are also supplied over a conductor 62 and througha bucket capacitor 53 (Fig. 2) of the first count subtraction circuit toa station selection switch 64; they are also supplied to the secondcount subtraction circuit through a coupling or blocking capacitor 66 oflarge capacity to a second station selection switch 61 which is gangedwith the switch 64 as indicated by the broken line 68, the two switchesbeing operated by the knob 65'.

At the switch 64, alternate switch contact points are connected to thefeedback conductor 26 whereby at these switch point positions the 20,000as. pulses are fed back to the divider |5 to subtract counts. It may bedesirable because of distributed or stray leakage in the switch 64 orcapacitor 63 to connect the switch arm 64 to ground through a l megohmresistor 55 to permit charges to leak off.

At the switch 61, the last six switch contact points are connected inpairs, the three pairs of contact points #t2-#3, #4-#5 and #6-#7 beingconnected through "bucket capacitors 1|, 12 and 1s,\respective1y, to thefeedback conductor 49 which leads to the second count subtractioncircuit. Thus, withv switch 61 in any one of the last six positions,20,000 as. pulses are applied to the divider 33 to subtract counts.

The cathode ray of tube |39 is deflected horizontally by either aslow-sweep or a fast-sweep deflecting wave that is in synchronism withthe 40,000 ps. square wave from the Eccles-Jordan oscillator 65 (Fig.1).

COUNT sUB'rRAc'rIoNs FOR STATION Y Y n SELECTION Referring now moreparticularly to the feature of subtracting counts for the purpose ofstation selection, specific pulse repetition rates for a plurality ofpairs of ground transmitters stations will be used by Way of example toaid in explaining the operation.

It will be assumed that the first pair of ground stations transmit the Apulses with a repetition period of 40,000 ps. and transmit the B pulseswith a like repetition period; that the second pair of ground stationstransmit A and B pulses having a repetition period of 39,900 as.; thatthe third pair transmits 39,800 as. pulses; that the fourth pairtransmits 39,700 ps. pulses, etc. It is apparent that for stationselection at the receiving apparatus, the operator must be able toselect corresponding repetition periods for the output of the squarewave generator 65 which controls the cathode-ray deection cycle; namely,periods of 40,000 as.; 39,900 as.; 39,800 as.; 39,700 ys.; 39,600 as.;etc.

It will be noted that the several repetition periods differ from eachother by 100 as. or by integral multiples thereof, and that thiscorresponds to repetition period differences of as. or integralmultiples thereof at the output of the frequency divider chain, i. e.,at the input of the clipper 60. Therefore, the desired repetition periodcan be obtained by shortening the 20,000 as. period by 50 as., by 100as., by 150 ps., etc.

For example, to obtain the 39,900 ps. repetition period the switches 64and 61 are moved to the #l switch contact points. At this switchposition the 20,000 ps. pulses from the lead 62 are fed back by way ofthe bucket capacitor 63, the switch 64 and the conductor 26 to thefrequency divider I6 only. Upon the occurrence of a 20,000 as. pulse, itproduces a pulse of current through the bucket capacitor 63 and throughthe diode 23 to add a charge to the storage capacitor 2|. At the end ofthe pulse, the capacitor 63 discharges through the diode 24 to itsoliginal potential. By properly selecting the capacity value of thebucket" capacitor 63, the added charge is made equal to the charge whichis added to the capacitor 2| by a single 50 as. pulse.` Thus, the 20,000as. pulse causes the blocking oscillator 22 to fire one pulse earlier or50 ps. sooner than it normally would whereby the desired repetitionperiod of 19,950 ps. at the clipper or 39,900 as. at the output of theE-J oscillator is obtained. It may be noted that, in the example given,each time a 20,000 ys. pulse occurs, the divider I6 divides by oneinstead of by two.

To obtain the 39,800 as. repetition period, the switches 64 and 61 aremoved to position #2. Now the 20,000 as. pulses are applied through thebucket capacitor 1| to the divider 33 and upon the occurrence of a20,000 as. pulse it applies a charge to the capacitor 39 through thediode 48. At the end of the pulse the capacitor 1| discharges throughthe diode 41 to its original potential. The capacitor 1| is given acapacity value such that this charge applied by the 20,000 as. pulse isequal to the charge applied by a single 100 as. pulse. Thus, upon theoccurrence of a 20,000 ps. pulse the blocking oscillator 4| fires onepulse early or 100 Ils. sooner than it normally would whereby thedesired repetition period of 19,900 as. is obtained at the clipper 60and a repetition period of 39,800 as. is obtained at the output of theE-J oscillator 65. It may be noted that in the example given, thedivider 33 divides of each 20,000 as. pulse.

To obtain the 39,700 ps. repetition period, the switches 64 and 6l aremoved to the #3 position, this being the switch position shown in thedrawing. Now the 20,000 lis. pulses are applied to both the divider I6and the divider 33 through the switches 64 and 61 whereby both dividerslose a count. Specifically, the blocking oscillators 22 and 4I ofdividers I6 and 33 fire 50 fis. and 100 as. early, respectively, or atotal oi 150 ps. early. Thus, the desired repetition period of 2 19,850lis. or 39,700 as. is obtained at the E-J oscillator output.

To obtain the 39,600 as. repetition period, the switches 64 and 61 aremoved to the #4 position. Again, the 20,000 as. pulses are applied tothe divider 33 only, but this time through the capacitor 12 which has acapacity value such that a. 20,000 as. pulse causes the divider 33 tolose two counts, i. e., to trigger 200 es. early. Thus, the desiredperiod of 2 l9,800 ps. or 39,6004 ps. is obtained at the E-J oscillator.

At the #5 switch position, the divider I6 again triggers 50 frs. earlyand the divider 33 triggers 200 ps. early, or a total of 250 its. forthe two dividers. Thus, the repetition period is 19,750 ps. at the inputto clipper 60 or 39,500 as. at the output of the E-J oscillator 65.

At the #6 switch position, only the divider 33 receives the 20,000 ps.pulses. These pulses are applied through the capacitor 13 which isadjusted to make the divider 33 lose three counts. Thus, it triggers 300as. early to give a repetition period of 2 l9,700 ys. or 39,400 as. atthe E-J oscillator output. I

At the #7 switch position, both of the dividers I6 and 33 lose counts,divider I6 triggering 50 frs. early and divider 33 triggering 300 ps.early, or a total of 350 frs. whereby the repetition period is 19,650as. at the clipper 60 or 39,300 ps. at the E-J oscillator output.

. It may be preferred to employ a different group of repetition periodsthan the group of 40,000 es., 39,900 ys., etc. assumed above. By makingthe nal divider stage 59 divide by three, for example, instead of byfour, the divider chain output pulses have a repetition period of 15,000ps. so that a group of repetition periods of 30,000 as., 29,900 ps.,etc. may be employed. Or the divider stage 59 may be made to divide byfive to obtain a group of repetition periods'of 50,000 ps., 49,900 ps.,etc.

In order to obtain a more rapid right drift of the A and B pulses in thepreliminary steps of obtaining a time difference reading, it may bedesirable to provide a capacitor 95 that may be connected by a switch 96to the coupling capacitor 66 so that by closing the switch 96 additionalcounts will be lost by the divider 33. Thus, the

Yby four instead of by five upon the occurrence 8 A and AB pulses may bedrifted toward the right by closing the switch 96. When the switch 36 isopened the A and B pulses stop drifting and again are stationary.

CATHODE RAY TRACE PRESEN'IATION Before describing that portion of thereceiving apparatus of Fig. 1 to vwhich the control pulses from thepulse generator unit are applied, reference will be made to Fig. 4.

In Fig. 4, the graphs X and W show the wave shapes of the slow-sweep andfast-sweep horizontal deecting waves, respectively, for obtaining thedesired cathode-ray traces. The wave V comprises a pair of recurringpulses; the second of which (referredV to as.Y the variable indexmarker) is adjustable in time and determines the starting time t of thewave f-g of the graph W. The starting time t of the variable indexmarker in relation to the fixed index marker may be adjusted byadjusting a sine wave phase shifter |00 by a knob |00' and by adjustingtwo delay circuits |0| and |02 by knobs |0I' and |02 (Fig. 1), as willbe explained hereinafter, for aligning the A and B pulses. Threeswitching positions identified as positions #1, #2 and #3 are usedsuccessively in aligning the A and B pulses. It will be understood thatwhile the pulses A and B and their corresponding fast-sweep tracesappear alternately on the cathode-ray tube screen, they appear to theeye to occur simultaneously because of persistence of vision, lag ofphosphorescence of the screen or both.

As shown in Fig. 4, the B pulse is the one that occurs after theInici-point of the A pulse period, and consequently the time interval,which elapses between the occurrence of a B pulse and the succeeding Apulse will be less than one half pulse interval. As will be seen in Fig.4, the start of one fast sweep (lL- i) coincides with the start of aslow trace, while the start of the other fast sweep (f-g) coincides withthe variable index marker.

As already explained a momentary change of the recurrence rate willchange the location of the pulses on the trace. Specifically, it ispossible for the operator to locate the A pulse at the left side of theupper slow trace, which in turn will cause the B pulse to fall on thelower trace, and the variable index marker may be madeto coincide withthe B pulse. Therefore. when the function switch is turned to position#2, the A pulse will occur during the trace described by the fixedfast-sweep deflecting wave h--i, while the B pulse will occur during thetrace described by the variable fast-sweep deflecting wave f-g.

A ilner adjustment will permit the operator to align the A and B pulsesso that the time elapsed between the start of the respective fast sweepsand the corresponding pulses are 'equal and occurs during the expandedparts of the traces,

thereby providing good accuracy for determining the time delay. Thisfeature is claimed broadly in copending application Serial No. 560,648,led October 27, 1944, now Patent No. 2,430,570, issued November 1l,1947, in the name of George D. Hulst, Jr., and entitled Radio NavigationSystem.

In the present system, after the A and B pulses have been aligned withthe receiver switched successively to operating positions #1, #2 and #3,the desired time difference or time interval is read off the veeder-rootcounters |03, |04, and |05 (Fig. 1) which indicate, respectively,microsecond units, hundreds of microseconds, and

thousands of microseconds. It will be apparent that the time intervalthus obtained is the amount that the starting time t of the variableindex marker has been delayed in time with respect to the mid-period d'(Fig. 4) of the deflecting wave cycle in order to align the A and Bpulses.

It may be noted that the upper fast trace h-i (illustrated in Fig. '1)is produced by the iirst fast-sweep Wave h-i of the deflecting wave W.The lower fast trace f-g (Fig. '1) is produced by the second fast-sweepWave f-g of the deflecting wave W.

DESCRIPTION OF CATHODE RAY TRACE PRODUCING CIRCUITS, ETC., OF FIG. 1

Before describing in detail the means for shifting the variable indexmarker, this means and other portions of the receiver system asillustrated in Fig. 1 will be described generally.

Referring to Fig. 1 and to the graphs of Fig. 4, the output of lthe20,000 as. blocking oscillator is supplied over a conductor Gla andthrough a polarity reversing transformer 60a and a lead 6|b to aslow-sweep deecting circuit H5 for producing a sawtooth voltage wave X.

The output of the clipper 60 is supplied over a lead 6| to theEccles-Jordan oscillator 65 whereby it is triggered by the 20,000 ps.pulses supplied thereto to produce a rectangular voltage wave whichappears unchanged at the output of a cathode follower tube I as the waveC.

To produce the fast-sweep deecting wave W, the Wave C is supplied over aconductor |98 to a differentiating circuit |05 to produce a pulse |05Athat appears later as the fixed index marker of the Wave V.

The circuit for producing the variable index marker of wave V will nowbe described generally with reference to Figs. l and 4. It will bedescribed in detail hereinafter with reference to the circuit diagram ofFig. 5. As previously indicated, it is the wave V that is applied to thefast-sweep deflecting circuit |22 for producing the fast-sweep wave W.

General description of circuit for producing the variable index markerReferring to Figs. l and 4, the wave C is supplied from the cathodefollower tube l5 to a clamp tube circuit l0* which applies a wave C' toa l0 kilocycle key oscillator |09. The oscillator |09 always starts upin a definite phase relation with respect to the front edge of thepositive half cycle of wave C to produce the 10 kc. sine wave D. Thispositive half cycle period is the one during which the pulse B occursand is referred to as the slave period. The wave D is supplied to acathode follower tube and appears unchanged at its output.

Next the Wave D is passed through a sine wave phase shifter |00 whichmay be of the goniometer type, and the phase shifted signal E is passedthrough a limiten ||2 to produce the rectangular pulses F. 'I'he pulsesF are applied to a blocking oscillator l I3 which produces the pulses Ghaving a 100 microsecond repetition rate. The oscillator l|3 triggers onthe front edges of the rectangular pulses F so that the pulses G occurpractically simultaneously with said front edges. It is evident thatshifting the phase of the wave E results in a shift in the timing of thepulses G.

The pulses G are applied to a 5 to 1 frequency divider |14 to obtain thepulses H having a 500 ps. repetition rate. The pulses H, in turn, are

l0 applied to a 2 to 1 frequency divider H6 to obtain the pulses Ihaving a 1000 as. repetition rate. The 1000 ps. pulses I are applied toa pulse selector circuit |20 where a particular pulse is selected asexplained hereinafter. f

Also, 100 ps. pulses G are supplied from the blocking oscillator H3 overa conductor Ill to a pulse selector circuit |18'. At the selector ||8.one of the 100 as. pulses of wave G is selected by means of a gate pulseT (Fig. 4). The selected pulse is represented by the wave U and issupplied over a conductor ||9 to the mixer |06. The mixed waves U and|05A pass through a clipper |2| and appear as the wave V which drivesthe fast-sweep deiiecting circuit |22 to produce the wave W.

By selecting a particular 100 ps. pulse and by shifting the timing ofthe selected pulse by means of the phase shifter |00, it is possible toadjust the timing of the variable index marker precisely and todetermine precisely by a direct reading what the timing is. Themicroseconds from 0 to 99 may be read from the counter |03 which ismechanically connected to the shaft of the phase shifter |00.

The microsecond readings in hundreds and in thousands are obtained fromthe counters |04 and |05 that indicate the settings of the delaycircuits |02 and |0|. These delay circuits comprise part of the gateproducing circuit that supplies the gate pulse T by means of which thedesired 100 as. pulse is selected at 118.

Reference to the graphs of 4 will show that the rst 100 as. pulse of thewave G occurs upon the occurrence of the second pulse of the wave F.Specically, the blocking oscillator ||3 is not permitted to trigger inresponse to the occurrence of the rst pulse of wave F with phase shiftsapproaching 360. The reason for this will be explained hereinafter. Thisresult is accomplished by utilizing a wave shaping circuit |25 that lsreferred to as a blocking Oscillator delay circuit. The circuit |25 hasthe wave C applied to it which it converts to the wave J.

The wave J is a negative pulse of adjustable amplitude and is applied tothe blocking oscillator ||3 solas to keep it blocked during theoccurrence of the firstpulse of the wave F. In order to adjust theamplitude of the pulse J as the phase of the Wave F is shifted, anadjustable element of the `oscillator delay circuit |25 is mechanicallycoupled to the rotor shaft of the phase shifter |00. This will beexplained more fully with reference to Fig. 5.

Referring now to the portion of the circuit that selects the desired as.pulse by means of the gate pulse T, the Wave C from the cathode follower|5 is supplied over a lead |26 to a clipper and diiferentiator circuit|21 to produce the wave K. The wave K is applied to the coarse delaycircuit |0| to trigger it on the positive pulse of the wave K. The delaycircuit |0| in the example illustrated is a phantastron, the details ofwhich will be described hereinafter with reference to Fig. 5.

The output of the phantastron |0| is the wave L which is passed througha clipping amplier |28 to produce the rectangular wave M. The back slopeof the wave L and, therefore, the back edge of the wave M may beadjusted by means of the knob |0 to vary it over a wide timing range.The wave M is differentiated by a differentiating circuit |29 to producethe wave N. The positive pulse of the Wave N triggers a rectangularpulse producing circuit |3| to produce a gate pulse 0.

The gate pulse is applied to the pulse selector circuit where aparticular 1000 as. pulse represented by the wave P is selected. Anydesired 1000 ps. pulse may be selected by adjusting the delay circuitI0| and thereby shifting the position of the gate pulse 0 along its timeaxis. The selected pulse P is applied over a conductor |32 to the iinedelay circuit |02 which, preferably, is also a phantastron. Its outputrepresented by the wave Q is passed through a clipping amplier |33 toproduce the rectangular wave R. The timing of the back edge of the waveR may be adjusted by means oi the knob |02' of the delay circuit |02.The wave R is dierentiated by a circuit |34 to produce the wave S whichis applied to a rectangular pulse producing circuit |36. The positivepulse of wave S triggers the circuit |36 to produce the gate pulse Twhich is applied to the pulse selector circuit 8.

The gate pulse T may be shifted along its time axis by adjusting thedelay circuit knob |02 so that any desired 100 as. pulse of wave G lyingbetween successive 1000 ps. pulses of wave I may be selected. Theselected 100 ps. pulse is represented by the wave U and is applied'overlead ||9 to the mixer |06 and the clipper |2| to produce the variableindex marker (of wave V) which determines the start of the fast-sweepwave f-g.

' From the foregoing it will be seen that sweep wave f-g can be adjustedor timed to align the A and B pulses by: l

(1) Adjusting the knob |0| to select a 1000 us. pulse.

(2) Adjusting the knob I 02' to select a 100 ps. pulse, and

(3) Adjusting the knob |00' to shift the phase of the selected 100 as.pulse.

It should be noted that an adjustment of the phase shifter |00 willnever shift the selected |00 ps. pulse out of coincidence with the gatepulse T. The reason for this is that the gate pulse T is shifted alongits time axis whenever the 100 ps. pulses are shifted in phase due tothe fact that the selected 1000 as. pulse is shifted in phase with the100 ps. pulses, and due to the fact that a phase shift in the selected1000 ps. pulse causes a shift in the pulse R which, .in turn, causes ashift in the phase of the gate pulse T.

Description of mzer 106, etc.

Referring to Figs. 1 and 10, the mixer circuit |06 and the clippingcircuit |2| function to clip off the negative pulses of the `wave |05Aand to mix the remaining clipped positive pulses with the pulses U.Thus, the Wave V is obtained at the output of the clipper-mixercombination. The mixer |06, which may consist of two vacuum tubes havinga common anode resistor as shown in Fig. 10, reverses the polarity ofthe pulses. The waves in the plate circuit of the mixer |06 are of equalamplitude due to operation of the tubes in a condition where grid andplate voltage approach equal amplitude. The width of the differentiatedincoming pulses is short compared to that of the plate pulses, the Widthof the latter being controlled by a capacitor-resistor combination inthe plate circuit and therefore being independent of the width of theincoming wave. This capacitor-resistor combination comprises a capacitorCI and the plate resistor RI.

The wave V is supplied to the fast-sweep deflecting circuit |22 shown indetail in Fig. 10 and described hereinafter. 'Ihe narrow negative pulsesvof wave V produce the fast-sweep wave W having the useful deflectingportions h--z and f-g. The defiecting waves W and X are applied from thecircuits |22 and H5 through a wave selecting switch |23 and through ahorizontal defleeting amplifier |24 to the horizontal deecting plates|38 of the cathode-ray indicator tube |39. As described in copendingapplication Serial No. 589,320, now Patent No. 2,445,361, issued July20, 1948, filed April 20, 1945, in the names of Garrard Mountjoy, GeorgeD. Hulst, Jr., and Earl Schoenfeld and entitled Radio NavigationSystem', the horizontal deilecting amplifier |24 may be provided with aswitch (not shown) for changing the bias on the amplifier tubes when thefunction switch is changed from the slow-sweep position to thefast-sweep position and vice versa, thereby insuring optimum efficiencyand undistorted gain from the amplifier tubes.

The switch |23 has three contact points and three corresponding switchpositions, referred to as operating positions, which are identied,reading clockwise, as positions #1, #2, and #3.

There are four other operation position switches, described hereinafter,that likewise have these three switch positions and which are gangedwith the switch |23.

Switch |23, when in operation position #1, functions to apply theslow-sweep wave X to the horizontal deiiecting Plates |28 and, when inoperation positions #2 and #3, functions to apply the fast-sweep wave Wto the deflecting plates |28.

Production of variable indem marker description of circuit diagram (Fig.5)

Referring to Fig. 5, the clamp tube |08 is a A means of controlling thevoltage supplied to the anode and screen of the oscillator |09.l Duringthe positive half cycle of the wave C a large current is drawn by theanode of |08. During the negative half cycle no anode current is drawn.This produces the waveform C'.

The positive half cycle of the wave C' (Fig. 4) is applied to thetransition oscillator |09 as its operating voltage and keys theoscillator to make it start oscillating upon the occurrence of thepositive half cycle. Thus the 10 kc. sine Wave D is produced. Theoscillator does not oscillate during the negative half cycle of the waveC'.

An important feature of the oscillator |09 is that, when keyed on, italways starts in the same phase so that the timing of the wave D withrespect to the Wave C is always the same.

' The circuit and operation of the transition oscillator are well knownand are described, for instance, in the Proceedings of the I. R. E. forFebruary 1939, vol. 27, page 88. Another suitable type of oscillator isthe resistor-capacitor oscil lator described in Patent 2,373,737, issuedApril 17, 1945, to Maurice Artzt.

The wave D is applied from the cathode follower to the phase shifter |00by way of a coupling capacitor 206 and a coupling impedance coil 201.The purpose of the coil 201 is, in conjunction with phase shifter |00,to present a resistive impedance to the cathode of The phase shifter |00is of the goniometer type and is designed as described and claimed incopending application Serial No. 677,450, filed June 18, 1946, nowPatent No. 2,442,097, issued May 25, 1948, in the name of Stuart W.Seeley and entitled Electrical Networks for Phase Shifters. The coils206 and 209 are the crossed stator coils of a goniometer. and the coil2|| is the rotor coil of the goniometer.

The stato; or cross coils 208 and 209 are in- Ieluded in two branches orarms with four branch network. The two branches include coils 209 and208 and also include a capacitor 2I2 and a resistor 2|3 respectively.

A third branch of the network comprises a resistor 2|4 which isconnected in parallel with the branch 209, 2|2.l The resistor 2|4 hasthe same resistance as resistor 2I3, and this resistance is equal to thereactance of the capacitor 2 I2 at the frequency of the signal source.

A fourth branch of the network includes af perature.

The phase shifted sine wave E has both positive and negative half cyclesclipped by the limiter ||2 to produce the wave F which triggers theblocking oscillator II3, thus producing the 100 ps. pulses G. 'Iheoscillator I I3 is of a well known type having transformer feed-backcoupling,

" shown at 2 I1, from the anode circuit to the' cathode circuit. 100 ps.pulses G are supplied from the anode of the tube of oscillator |I3 tothe frequency divider II4. Also, 100 as. pulses G are supplied from the+B side of the primary of the transformer 2|1 over a conductor 2I8 tothe pulse selector I8.

The oscillator delay circuit |25 for producing the wave J is adifferentiating circuit consisting of a capacitor 2|9 and resistors 22|and 222 in series therewith. A shorting tap 223 on resistor 222 iscoupled to the rotor of phase shifter so that as the first pulse of WaveF is shifted to the right on the time axis, the amplitude of the pulse Jis increased. The wave J is applied with negative polarity through aresistor 224 to the grid of the tube of oscillator I I3. So long as thepulse J holds this grid negative a certain amount, the oscillator I|3will not be triggered by the wave F.

The reason for the above-described use of the pulse J is that without itthe oscillator I3 might not staydocked in on the correct triggeringpulse of wave 'F as the phase shift approaches a iull 360 shift. Thatis, the blocking oscillator might jump from a lock-in on the desiredpulse to a lock-in on an adjacent earlier pulse, for example, the rstpulse of wave F.

'Ihe frequency dividers ||4 and |I6 may be of any suitable type. In theexample illustrated they are of the same general type employed in thetimer chain of dividers (Fig. 2) but with the blocking oscillators ofthe type using anode circuit to cathode circuit coupling. Also, certaincircuit improvements will be apparent from the following description.

The frequency divider I|4 comprises the well known counter sectioncomprising a small capacity capacitor 226 and a large capacity storagecapacitor 221. Capacitor 221 receives a certain charge through a diodesection 228 each time a 100 ps. pulse occurs. At the end of the 100 ps.pulse the capacitor 226 discharges through the diode section 229. In thepresent 5 to l divider, the occurrence of the fifth 100 as. pulse raisesthe charge on capacitor 221 to a value that triggers the blockingoscillator 23| to produce a pulse of wave H. At the same time thestorage capaci- 14 tor 221 is discharged through the grid-cathodeimpedance of the blocking oscillator tube 232.

The point at which the oscillator 23| triggers is determined in part bythe setting of a bias tap 23g, the bias being applied through a leakresistor 23 The anode circuit of tube 232 is feed-back coupled to thecathode circuit by a transformer 236. The blocking oscillator is biasedso that it is not free running. this biasing being adjustable both atthe tap 233 and at a tap 231. Adjustment of the tap 231 adjusts the biason the grid of a cathode follower tube 238 and the cathode of the tube238 assumes a like bias, thus setting the bias of the cathode of theoscillator tube 232.

A cathode follower is used so asY to eliminate the use of a highresistance voltage divider to control the bias of the blockingoscillator.

The input impedance of the cathode of the cathode follower tube 238 hasa low resistance so that no substantial voltage can build up across theby-pass capacitor 239, which in the example illustrated has a capacityof 0.1 microfarad. Otherwise the triggering time of the oscillator 23|might vary due to some biasing voltage being built up across the by-passcapacitor 230 during the 20,000 ps. period that the divider II4 isproducing the ps. pulses.

The frequency divider IIB is similar to the divider II4 but has no biasvoltage applied to the grid of the oscillator tube 24|, the adjustablecathode bias controlled by the tap 242 proriding suicient adjustment.Also, it will be noted. that here the cathode follower tube is omitted,the bias being applied directly from the tap 242 to the cathode of theoscillator tube 24|.

The storage capacitor 243 of the counter circuit is shunted by `a leakresistor 244 of 6.8 megohms in the present example. This permits anycharge left on the capacitor 243 at the end of a 20,000 lis. slaveperiod (the keyed on period) to leak off before the next slave periodoccurs. Otherwise, at the start of a keyed on or slave period thecapacitor 243 might have a charge on it due to the occurrence of one 500ps. pulse immediately following the triggering of the oscillator 24|,this one 500 as. pulse being the last occurring pulse in the precedingkeyed on or slave period. The resistor 234 performs a similar functionin the divider I I4.

'Ihe 1000 as. pulses from the divider I|6 are supplied with negativepolarity over a conductor 26| to the cathode of a vacuum tube 262comprising the pulse selector |20. The gate pulse O is supplied withpositive polarity to the grid of the tube 262 whereby a 1000 ps. pulse Pis passed by the tube 262 if the gate pulse O is made coincidenttherewith.

The gate pulse O is produced as follows. Some of the E-J signal C issupplied to the clipper |21 comprising an amplifier tube 263 that isdriven hard enough to further square up the wave C. This squared-up waveis applied from the anode of the tube263 through a differentiatingcircuit comprising a capacitor 264 and a resistor 266. The resultingwave K appears across resistor 266 and the positive pulse thereoftriggers the coarse delay phantastron |0| to produce the wave L at itsoutput.

'Ihe phantastron |0| comprises a pentagrid tube 261., a triode 268 and adiode 269 connected as shown. The output wave L is taken olf the cathodeof tube 260 and has a linear descending portion having a duration thatis determined by the point or tap on a control potentiometer 21| towhich the cathode of the diode 269 is connected. Thus, the position ofthe back edge of the wave L is determined by adjusting the knob Thephantastron circuit is described in Electronics for May 1946, pages 142and 143.

The operation of the phantastron delay circuit may be describedasfollows:

1. Initial conditions or stage VI.-In the static condition of thephantastron tube 261, grid No. 1 is at cathode potential and no currentows to the plate of the tube. Electron flow to the plate is blocked bygrid No. 3 which is at a less positive potential than grid No. 2. Thissets up a negative field between grids No. 2 and No. 3, which blockselectron flow past grid No. 3 by counteracting the accelerating positiveeld from the cathode and grid No. 1 to grid No. 2. Therefor, tubecurrent flows to grid No. 2 under control of grid No. 1. The platepotential is set by the control potentiometer 21| connected to the plateof tube 261 through the diode 269. The voltage drop in the high-plateresistor of tube 261 holds the plate voltage at essentially the value towhich the control potentiometer is set.

2. Sage I.-A positive pulse is applied to grid No. 3 so that the blockedelectrons may flow past grid No. 2 to the plate. The rising platecurrent causes a falling plate potential which is coupled back to gridNo. 1 via the coupling capacitor 212, producing regenerative feedback.This results in a rapid reduction in plate and grid potential to the point at which a further drop would tend to cut oi plate current andcause plate voltage to start rising again. This stops the regenerativeaction and blocks further fall 1n grid No. 1 voltage. The drop in plateand grid voltage and the time involved is essentially independent of thestarting voltage of the plate, set by the control potentiometer 21|. Itis important to note that as soon as the phantastron tube plate voltagedrops below the level of the cathode voltage of the diode 269, the diodeceases to conduct and does not load down the phantastron plate circuit.

3. Stage II.-At the end of stage I, -grid No. 3 has lost control ofplate current now and control is exerted by grid No. 1 in the normalfashion.

Since grid No. 1 is tied to B+, it attempts to rise exponentially towardB| as the coupling capacitor 212 discharges. However, since grid No. 1is now controlling plate current, the plate voltage drops and opposesthe grid voltage change through the coupling capacitor. This negativefeedback reduces the rate at which grid No. 1 can rise and makes therate of change essentially linear. The linearity is also improved by thenegative feedback developed across the cathode resistor 213. At the sametime that grid No. 1 is rising, the cathode and grid No. 2 are risingand falling respectively, approaching the point at which grid No. 3 canagain block plate current. Since the point at which control of platecurrent switches back from grid No. 1 to grid N0. 3

l is xed by the constants of the circuit, the period during whichnegative feedback produces a linear rate of fall of plate voltage is adirect function of the starting plate voltage, set by the controlpotentiometer 21 I. The -rate at which grid No. 1 voltage rises andplate voltage falls is largely determined by the values of the grid No.1 resistor, the coupling capacitor 212, and the amplification of thetube 261.

4. Stage III .-At the 'end of stage II, the cathode has risen and gridNo. 2 has fallen sufiiciently to permit grid No. 3 again to assumecontrol of plate voltage. During the time that control of plate currentis switching from grid No. 1 to grid N o. 3, the plate current levelsoil.' .and does not change appreciably as grid No. 1 continues t0 rise.This eliminates the negative feedback and permits grid No. 1 to risemore rapidly as the plate voltage fall ceases. This constitutes stageIII. The duration of stage III is fixed by the constants of the circuitand is not affected by the static plate voltage.

5. Stage IV.-At the end of stage IU, grid No. 3 starts cutting off platecurrent ow, causing the plate Voltage to rise. The rising plate voltagecouples backy to grid No. 1, speeding up the action and again providingpositive or regenerative feedback. The cathode and grid No. 1 riserapidly to their original levels, grid No. 2 drops to its static level,and plate current ceases to now.

This constitutes the end of the time delay inter.

val since the jump in cathode voltage is used as the terminating pointin the cycle. The duration of stage IV is essentially constant, fixed bythe constants of the circuit.

6. Stage V.-At the end of stage IV, the plate voltage of the phantastrontube 261 does .notV immediately return to its initial static stagevalue, although plate current ceased to iiow. This situation existsbecause of the stray capacitors from the plate to ground. The return ofthe phantastron plate voltage to its static level at the end of stage IVis delayed only a negligible amount by the charging of tube and wiringcapacitance. At the end of stage V, the circuit has returned to theinitial stage and awaits another trigger pulse.

7. Summary 0f phantastron operation.-The time delay interval consists ofstages I, II, III, and IV. The duration of stages I, III, and IV issmall and is ixed by the constants of the circuit. The duration of stageII depends in linear fashion upon the plate voltage of the phantastrontube 261 at the start of the cycle. There is, therefore, a linearrelationship between the voltage applied by the control potentiometer21| and the total delay time. The output of the circuit is the negative,square-type voltage wave L with variable trailing edge developed at thecathode of tube 268. In general, this must be amplified anddifferentiated to obtain a variable delay pulse. An advantage of thecircuit in addition to the linear relationship between control voltageand delay time is the fact that it is relatively insensitive to slightchanges in supply voltage. The controlling voltages to the various tubeelements are all derived from the same B+ supply and the effect ofchanges in the supply is largely selfcompensating.

The wave L from the phantastron |0| is applied to the grid of theamplifying and clipping tube |28 to produce the rectangular wave Mhaving a back edge that may be shifted along the time axis by means ofthe knob |0|". The wave M is passed through the transformer |29 whichapplies the resulting differentiated wave N to the grid of the tube 216in the gate pulse producing circuit |3|.

The gate circuit |3| is a cathode coupled multivibrator that goesthrough one cycle of operation when triggered and then is inactive untilagain triggered. It comprises the tube 216 and a. tube 211, the tubeshaving a common cathode resistor 218. The positive pulse o`f Wave Ntriggers the gate circuit |3| to produce the gate pulse O at the anodeof the tube 211. The pulse O is then applied through a couplingcapacitor 219 to the 1000 as. pulse selector |20.

It will be evident that by operating the delay control knob I| the gatepulse O may be shifted in phase or timing so as to select any desiredone of the 1000 as. pulses I. Such a selected pulse P is supplithrough atransformer 28| and over conductors |32 to the ne delay phantastron |02.

The phantastron delay circuit |02 comprises a pentagrid tube 232, atriode 203. a diode 284 and a control potentiometer 234. The delaycontrol knob |02 operates a 10-position switch for connecting thecathode of the diode 234 to any one of ten taps on the potentiometer286. The circuit of the line delay phantastron |02 is the same as thatof the coarse delay phantastron |0| except for the change in circuitconstants required for producing the precise phase shift over thesmaller time range through which the fine delay phantastron operates.

The wave Q from the phantastron |02 is passed through an amplier andclipper tube |33 to obtain the rectangular wave R. The wave Ris thendifferentiated by the transformer |34 to produce the wave S. Thepositive pulse of wave S triggers the circuit |30 to produce the gatepulse T. 'Ihe circuit |30 is similar to the gate circuit |3| but hasdiil'erent circuit constants so as to produce a narrower gate pulse.

The gate pulse T is applied with positive polarity to the grid or thetube 231 of the 100 lis. pulse selector ||3. The 100 ps. pulses G areapplied by way of conductor 2|! to the cathode of the tube 231 withnegative polarity. Thus, any desired 100 ps. pulse such as the pulse Umay be passed through the pulse selector H8 by making the este puise 'rcoincident with the desired 100 as. pulse.

The pulse U is amplified by an amplier tube 233 and supplied overconductor ||3 to produce the variable index marker of the wave V aspreviously described.

While the coarse delay circuit |0| and the iine delay circuit |02 havebeen shown and described as phantastron circuits, it should beunderstood that while they are preferred circuits at the present'timethey may be replaced by delay multivibrators if desired. Suitable delaymultivibrators are well known in the art.

The wave `V. is supplied both to the fast-sweep circuit |22 and to theupper vertical deilecting plate 303 oi the tube |39. The connection forsupplying wave V to deecting plate 363 is by way of a conductor 333, aswitch 350. a resistor 384. thc conductor 30| and the capacitor 382.

In Fig. the values of certain circuit elements have been indicated,merely by way of example, in ohms, megohms, and micro-microfarads.

The fast-sweep deecting circuit |22 that is driven by the wave V(comprising the fixed and variable marker pulses) to produce thefast-sweep wave W will now be described with 'reference to Fig. 10.

The fast-sweep circuit Referring more specically to the circuit |22 (orproducing the fast-sweep wave W, as shown in Fig. l0 the circuitcomprises a vacuum tube 3|G and a pulse shaping network that comprisestwo sections consisting of cathode resistors 33| and 332 shunted bycapacitors 333 and 334, respectively, identified as network sections3|1a and 3|1b. The shaping network further comprises a delay linesection 3|`|c comprising series resistors 336 and shunt capacitors 331connected across the cathode resistor 33| and terminated in a resistor333 and in the cathode resistor 332.

18 The fast-sweep wave W is taken on the resistor 330 through anadjustable tap 330, the setting of which determines the amplitude of thewave W.

` In operation, the capacitors of the network sections 3|1a and 3|`|bare charged through the anode resistor 34| and the tube 3|0 to a certainvoltage level between successive pulses of the wave J to bring the tap330 to the voltage el. Upon the occurrence of each negative pulse oi thewave V, the tube 3|0 is driven to cut-oil and the capacitors 333 and 334discharge through the resistors 33| and 332, respectively. The section3|`|a comprising capacitor 333 and resistor 33| has a fast time constantwhereby the discharge of capacitor 333 produces a voltage of steep slopeacrossresistor 33|. The section Illa. comprising capacitor 334 andresistor 332 has a slower time constant whereby the discharge ofcapacitor 334 produces a. voltage of less slope across resistor 332.These two voltages of different slopes appear at the tap 339 as the sumof the two voltages with the voltage of the steeper slope slightlydelayed by the delay network section 3||c.

The wave form of the wave W following the said slight delay isapproximately logarithmic.

It should be understood that the fast-sweep wave W need not be of thewave form described and, in fact, may be linear although some form ofincreased expansion at the left end of the fast-sweep trace must beprovided for the occurrence desired in the present embodiment of theinvention. Such expansion may be obtained by employing either alogarithmic wave shape or an exponential wave shape, for example.

The above-described fast-sweep deilecting circuit is described andclaimed in application Serial No. 583,255, now Patent No. 2,403,969,issued March 8, 1949, filed March 17, 1945, in the name of George D.Hulst and entitled Cathode Ray Deflection Circuit.

As previously noted, the starting time t of the fast-sweep wave f-g isdetermined by the adjustment of the ps. pulse U (and in turn by thevariable index marker of wave V) whereby the start of the wave f--g maybe made to precede the received B pulse by the same amount that thestart of the wave h-i precedes the received A pulse, this being thecondition of alignment of the A and B pulses. It should also be notedthat Ythe wave f-g is identical with the wave h-i whereby exactalignment of the A and B pulses on the cathode-ray traces is obtained(as shown in Fig. 8) when the above-described timing relation exists.

An improved fast-sweep circuit described and claimed in copendingapplication Serial No. 674,184, now Patent No. 2,449,169, issuedSeptember 14, 1948, ied June 4, 1946, in the names of Paul F. J. Holstand Loren R. Kirkwood and entitled Defiecting Circuits, maybe employedif desired.

The slow-sweep circuit necting the lower end of cathode resistor 342 tothe junction point of a pair of bleeder resistors 3|3 and 320. 'Thisprevents the tube 3|8 from drawing current at the end of the sawtoothcycle so that flattening of the sawtooth wave is avoided.

19 The operation' is as follows: Each time one of the positive 20,000as. pulses from the lead Bla is supplied through a polarity reversingtransformer 63a (Fig. l) and a lead 6| b to the grid of the tube 3H byway of acoupling capacitor 32|. vthe capacitor 343 is charged suddenlyfrom the anode voltage supply through the tube 3|8 to a certain voltagelevel to bring the tap 344 to the voltage level e: (Fig. 4). At the endof each positive pulse, the capacitor 343 discharges slowly through theresistors 342 and 3|3 thus producing successively the slow-sweepsawtooth wave portion a-b and the sawtooth wave portion c-d at the tap344.

In Figs. 9 and 10 the values of certain circuit elements have beenindicated, merely by way of example, in ohms, megohms, microfarads andmicro-microiarads.

The radio receiver The A and B pulses from a pair of ground stations(Fig. 3) vare received by a radio receiver of the superheterodynetypezcomprising a radio frequency amplifier indicated at 36 a converter362, an I.F. amplifier 363 and a second detector and video frequencyamplier 364. The A and B pulses are supplied with positive polarity overa conductor 366. a conductor 38| and a capacitor 382 to the uppervertical deflecting plate 368. Thus, the A and B pulses may be made toappear, as shown in Figs. 6, '7 and 8, on the horizontal cathcde=raytraces. The A and B pulses are made to appear with equal amplitude onthe cathoderay tube screen by employing a differential gain controlcircuit described hereinafter.

Slow-sweep and fast-sweep trace separation The slow-sweep traces a--band c-d are separated as illustrated in Fig. 6 while the receiver is onthe #l operation position by means of the rectangular wave C (Fig. 1)supplied from the cathode follower tube I (Fig. 1) over a conductor 363to the #i contact point of a trace separation switch 31|, and over aconductor 312 to the upper deflecting plate 368 oi the cathode ray tube|38. Thus, the portion of the wave C, which is positive as it appearson" the upper plate 368, holds the cathode ray deflection up a certainamount during the occurrence of the slow-sweep deecting wave c-d. Thefast-sweep traces f-g and h--i are separated as illustrated in Fig. 7during the #2 operation position also by means of the rectangular waveC.

Fast-sweep blanlcing Blanking is provided so that only the traces j--gand h-i appear on the cathode-ray screen when in the #2 and #3fast-sweep operating positions. This blanking is provided by means ofthe negative portions of the wave Y as it appears on the anode of thetube 3|6 (Fig. 10) of the fast-sweep detlecting circuit |22. The wave Yis supplied from the anode of tube 3|6 to the #2 and #3 contact pointsof a switch 32| whereby in the #2 and #3 operation positions, this waveis supplied over conductors 322 and 326 to the grid 321 of the cathoderay tube |39.

Trace brilliance control nected across the diode 324 and the cathode ofthe 20 diode 324 is connected to a variable bias voltage source (notshown) In operation, during the periods that the blanking waves arepositive at the anode of the diode 324. the impedance of the diode 324is very low so that its anode is practicallyat the bias potential of itscathode. Thus, regardless of the form of the blanking wave andregardless of whether any blanking wave is being applied, the voltage onthe grid 321 of the cathode ray tube during the cathode-ray sweeps issubstantially the voltage on the cathode of the diode 324.

DIFFERENTIAL GAIN CONTROL CIRCUIT A differential gain control circuitfor the R.F. vamplifier 36| of the radio receiver preferably isprovidedl as shown in Fig. 1. for the purpose of keeping the amplitudesof the A and B pulses substantially alike at the receiver output, thusfacilitating the A and B pulse alignment. The gain control circuitincludes a resistor 343 connected between the anodes of the two tubes ofthe E-J oscillator 65. An adjustable differential gain balance tap onresistor 243 may be moved to either side of the center thereof todecrease the gain of the R..-F. amplier 36| during either the receptionof the pulse A or the pulse B. The voltage at the gain balance tap issupplied through a capacito-r 344 and a resistor 346 to the anode of adiode 341 and to the #2 and #3 contact points of a differential gaincontrol switch 348. Thus, when the receiver is oneither the #2 or#S'operation position for pulse alignment on the fast sweeps, thedierential gain control voltage is applied through the switch 348 and aconductor 343 to the gain control grid of an ampliiier tube in the R.F.am-

plifler 36|.

'I'he diierential gain control operation with the receiver on either #2or #3 operation position is as follows:

When the gain balance tap is at the center of resistor 343, no voltagewave is applied to the diode 341. When the tap is on one side of thiscenter or balance position, a wave of one polarity is applied to thediode 341; when the tap is on the other side of the balance point, awave of the opposite polarity is applied to the diode 341. The diode 341functions to supply a negative bias during the negative half cyclefollowing a positive cycle of an applied wave. For example, a positivehalf cycle causes diode current to charge capacitor 34411, and duringtheefollowing negative half cycle the capacitor 344a discharges slowlythrough a resistor 35| connected across the diode 341 thus making theanode of diode 341 negative with respect to ground and reducing the gainof the I.F. ampliiler 362 while the B pulse (or the A pulse) is beingamplified.

. With switch 348 on the #1 operation position for pulse alignment,normal operating bias voltage V isv on the R.-F. amplifier 362.

PROCEDURE IN MAKING A TIME MEASURE- MENT The successive steps in makinga measurement of the time interval between the A and B pulses from apair of ground stations will now be described.

stationary onthe two traces a-b and c-d. A suitable drift switch such asswitch 96 (Fig. 2)

2l or knob Il o'f oscillator ll is operated to drift one of the pulsesonto the upper trace c-d and over the nxed index marker at the left endof this trace. The other pulse will now appear on the flowertracea-b.Thepulseonthetracec-d.

istheApulseandthepulseonthetraceo-b is the B pulse. That this is truewill be evident by referring to the graphs of Fig. 4.

Next, the starting time t of the variable index marker of wave V isadlusted by operating the phase shift and delay controls ill', lll' andill' of the phase shifter Il! and the phantastrons III and Il! (Figs. land 5) to bring the variable index marker under the B pulse. Thevariable index marker is now carefully adjusted so that its positionwith respect to the B pulse is substantially the same as the position ofthe iixed index 4marker with respect to the A pulse.

Position #2 Next, referring to Fig. 7, the receiver is switched to thefast-sweep operation position #2 which results in the A and B pulsesappearing on the traces h-t and f-o respectively. As shown in Figui, thestart of the variable index marker Position #3 'I'he final alignmentofthe `.A and B pulses is done on operation position #3 with the twotraces f--g and h-i superimposed as shown in Fig. 8. 'Ihe front edges ofthe A and B pulses are now exactly aligned (they usually difier slightlyin shape) by operating the-knob Ill' of the phase shifter |00. The timereading can now be made from the counters N3, I and lli.

For example, if the counters IIS. i and I read 6, 8 and 42,respectively, the reading is 8842 microseconds.

I claim as my invention:

1. In a radio system wherein periodically recurring A pulses and Bpulses are received from ground stations and wherein two similardeflecting waves, one of ilxed timing and the other of adjustabletiming, are to be produced for deflecting the cathode ray of a cathoderay tube indicator, said A pulses having the same repetition period assaid B pulses. means for producing a square wave having the samerepetition period as said A and B pulses, the half cycle of said squarewave that occurs during the occurrence of a B pulse being identified asthe slave period, means for producing a sine wave signal having a iixedphase with respect to said slave period, a phase shifter through whichsaid sine wave signal is passed to obtain a phase-shifted wave, meansfor converting said phase-shifted wave to periodically recurringshort-duration timing pulses, means for selecting a. desired one of saidtiming pulses, and means for producing said adjustable deilecting wavein response to the occurrence of said selected pulse whereby saidadjustable deilecting wave maybe shifted to a desired position along atime axis by selecting adesired timing pulse and by 22 sluiting thephase of the selected timing pulse by said phase shifter.

2. The invention according to claim 1 wherein said means for producing asine wave signal having a ilxed phase with respect to the slave periodcomprises a sine wave oscillator of the type that always produces a sinewave sigml starting in a deilnite phase relation in response to beingkeyed into an oscillatory condition and wherein said means furthercomprises keying means for keying said oscillator into an oscillatorycondition simultaneously with the occurrence oi said slave period andfor the duration only of said slave period.

3. In a radio navigation Vsystem wherein periodically recurring A pulsesand B pulses are received from ground stations and wherein a variableindex marker is to be produced. said A and B pulses having the samerepetition period, means for producing a square wave having the samerepetition period as said A and B pulses. the half cycle of said squarewave that occurs during the occurrence of a B pulse being identiiled asthe slave period, means for producing a sine wave signal having a xedphase with respect to said slave period, a phase shifter through whichsaid sine wave signal is passed to obtain la phase-shifted wave. meansfor converting said phase-shifted wave to periodically recurringshort-duration timing pulses, means for selecting a desired one of saidtiming pulses, and means for causing said selected pulse to produce avariable index marker which may be shifted to a desired position byselecting a desired timing pulse and by shifting the phase of theselected timing pulse by said phase shifter.

4. In a radio navigation system wherein periodically recurring A pulsesand B pulses are received from ground stations and wherein a ilxed indexmarker and a variable index marker are to be produced. said A and Bpulses having the same repetition period, means for producing a squarewavelhaving the same repetition period as said A and B pulses, the halfcycle of said square wave that occurs during the occurrence of a B pulsebeing ldentied as the slave period, means for producing a sine wavesignal having a fixed phase with respect to said slave period, a phaseshifter through which said sine wave signal is passed to obtain aphase-shifted wave, means for limiting said phase-shifted wave forproducing rectangular pulses. means for converting said rectangularpulses to short-duration timing pulses, means for selecting a desiredone of said timing pulses, and means for causing said selected pulse toproduce a variable index marker which may be shifted to a desiredposition by selecting a desired timing pulse and by shifting the phaseof the selected timing pulse by said phase shifter.

5. In combination, means for producing pulses having a certainrepetition rate, means for producing other pulses having a repetitionrate that is a submultiple of said rst repetition rate, a pulse selectorcircuit to which said submultiple rate pulses are applied, variabledelay means for producing a gate pulse that is applied to said selectorcircuit for selecting a desired 'one of said submultiple rate pulses, asecond pulse selector circuit to which said first pulses are applied, asecond variable delay means to which said one selected submultiple ratepulse is applied and comprising means for producing a pulse having afront edge that occurs in response to 7| the occurrence of said oneselected submultiple rate pulse and having a back edge that isadjustable in timing,` means for producing a second gate pulse inresponse to the occurrence of said adjustable back edge, and means forapplying said second gate pulse to said second pulse se-, lector forselecting a desired one of said rst pulses.

6. In a radio navigation system, means for producing pulses having arepetition period of 100 microseconds, means for producing other pulseshaving a repetition period ot 1000 microseconds, a pulse selectorcircuit to which said 1000 microsecond pulses are applied, variabledelay means for producing a gate pulse that is applied to said selectorcircuit for selecting a desired one of said 1000 microsecond pulses, asecond pulse selector circuit to which said 100 microsecond periodpulses are applied, a second variable delay means to which said oneselected 1000 microsecond pulse is applied and comprising means forproducing a pulse having a front edge that occurs in response to theoccurrence of said one selected 1000 microsecond pulse and having a backedge that is adjustable in timing, means for producing a second gatepulse in response to the occurrence of said adjustable back edge, andmeans for applying said second gate pulse to said second pulse selectorfor selecting a desired one of said 100 microsecond period pulses.

7. In a radio navigation receiving system for measuring the timeinterval between two received radio pulses A and B, the A pulse beingtransmitted at a periodic rate from a master ground station and the Bpulse being transmitted at said periodic rate from a slave groundstation, means for producing a square wave having the same repetitionperiod as said A and B pulses and having a master half cycle or periodthat occurs during the reception of said A pulse and having a slave halfcycle or period that occurs during the reception of said B pulse, meansincluding a frequency divider chain for producing timing pulses having acertain repetition rate and which pulses having a repetition rate thatis a submultiple of said rst repetition rate, a pulse selec-l torcircuit to which said submultiple rate pulses are applied, variabledelay means for producing a gate pulse that is applied to said selectorcircuit for selecting a desired one of said submultiple rate pulses, asecond pulse selector circuit to which said rst timing pulses areapplied, a second variable delay means to which said one selectedsubmultiple rate pulse is applied and comprising means for producing apulse having a front edge that occurs in response to the occurrence ofsaid one selected pulse and having a back edge that is adjustable intiming, means for 6 producing a second gate pulse in response to theoccurrence of said adjustable back edge, means for applying said secondgate to said second pulse selector for selecting a desired one of saidfirst timing pulses, means for simultaneously varying the phase ortiming of said selected first timing pulse and said selected submultiplerate pulse, a cathode ray tube having a screen, a deflecting wavegenerator for producing a pair of deflecting waves which are applied tosaid tube to produce a pair of cathode-ray traces on said screen,lmeansfor applying said A and B pulses to-said cathode ray tube whereby theyappear on said two traces, respectively, means for producing one of saiddetiecting waves in a certain time relation to the start of said masterperiod, and means for producing the other of said deilecting Waves inresponse to the occurrence of said selected rst timing pulse whereby thetiming 0f`said other deflecting wave may be adjusted to bring the A andB pulses appearing on said two traces into alignment.

8. In a radio navigation receiving system for measuring the timeinterval between two received radio pulses A and B. the A pulse beingtransmitted from a master ground station and the B pulse beingtransmitted from a slave ground stations, means for producing a squarewave having the same repetition period as said A and B pulses and havinga master h alf cycle or period that occurs during the reception of saidA pulse and having a slave half cycle or period that occurs during thereception of said B pulse, means including a frequency divider chain forproducing pulses having a 100 microsecond repetition period, means forapplying said square wave to said divider chain to make it active onlyin response to and during said slave period wnereby said 100 microsecondperiod pulses always occur in a definite time relation to the start ofsaid slave period. means for producing from said divider chain otherpulses having a 1000 microsecond repetition period, a pulse selector towhich said 1000 microsecond period'pulses are applied, variable delaymeans forsupplying a variable gate pulse to said pulse selector forselecting a desired 1000 microsecond period pulse. a second variabledelay means .to which said selected 1000 microsecond period pulse isapplied.

said second delay means comprising means for producing a gate controlpulse in response to the occurrence of said applied 1000 microsecondperiod pulse, means for varying the timing of the back edge of said gatecontrol pulse, means for producing a second variable gate pulse inresponse to the occurrence of said variable back edge. a second pulsevselector circuit to which said second gate pulse is applied, means forsupplying to said second pulse selector pulses from said frequencydivider of 100 microsecond repetition period, whereby a desired 100microsecond period pulse may be selected by varying the timing of saidsecond gate pulse, means for varying the phase or timing of saidselected 100 microsecond period pulse, a cathode ray tube having ascreen, a delecting wave generator for producing a pair of deectingwaves which are applied to saidtube to produce a pair of cathode-raytraces on said screen, means for applying said A and B pulses to saidcathode ray tube whereby they appear on said two traces, respectively,means for producing one of said deilecting waves in a certain timerelation to the start of said master period, and means for producing theother ot said deflecting waves in response to the occurrence of saidselected 100 microsecond period pulse whereby the timing of said otherdeflectng wavevmay be adjusted to bring the A and B pulses appearing onsaid two traces into alignment.

9. In a receiver for a radio navigation system wherein an A pulseistransmitted from a master ground station and a B pulse is transmittedfrom a slave ground station, means comprising a timing oscillatorfollowed by a chain of dividers for producing a square wave having arepetition rate corresponding to that of the received ground stationpulses, the half cycle of the square wave that occurs during theoccurrence of a B pulse being u identified as the slave period. acathode ray tube having a screen, means for producing a pair ofslow-sweep traces on said screen, means for making the received A and Bpulses appear on said traces, means for determining approximately thetime difference between said A and B pulses while they appear on saidslow-sweep traces, means for producing a pair of fast-sweep traces thatoccur during the duration of said A and B pulses, respectively, meansfor adjusting the timing of one of said fast-sweep traces for obtainingalignment of said A and B pulses as they appear on said fast-sweeptraces, said last means comprising means for supplying a sine wavesignal that always has a fixed phase relation with respect to the startof said slave period, a phase shifter through which said sine wavesignal is passed to shift its phase, a pulse producing circuit to whichsaid phase shifter output is applied to produce pulses having a 100microsecond repetition period, a 100 microsecond pulse selector circuitto which said 100 microsecond pulses are applied, a frequency dividercircuit to which said 100 microsecond pulses are applied for producingpulses having a 1000 microsecond repetition period, a 1000 microsecondpulse selector to which said 1000 microsecond pulses are applied, acoarse variable delay means for producing a gate pulse occurring onceduring each slave period and adjustable in timing, said gate pulse beingapplied to said 1000 microsecond selector circuit whereby a desired oneof said 1000 microsecond pulses is selected, a iine variable delay meansto which said selected 1000 microsecond pulse is applied for producing agate pulse that may be shifted in time between successive 1000microsecond pulses for selecting a desired 100 microsecond pulse, meansfor applying said last gate pulse to said 100 microsecond pulse selectorwhereby a desired one of said 100 microsecond pulses is selected, meansfor applying said selected 100 microsecond pulse to said fast-sweeptrace producing means and for causing the one of said fast traces thatoccurs during a B pulse to start in response to the occurrence of saidselected 100 microsecond pulse whereby exact alignment of said A and Bpulses may be obtained by adjusting said coarse delay' circuit, saidfine delay circuit, and said sine wave phase shifter.

MILTON J. MINNEMAN.

REFERENCES CITED The following references are of record in the le ofthis patent:

UNITED STATES PATENTS Number Name Date 2,403,600 Holmes July 9, 19462,405,238 seely Aug. 6, 1946 2,423,523 Shumark et al July 8, 19472,430,570 Hulst Nov. 11, 1947 2,432,158 Hulst et al Dec. 9, 1947 OTHERREFERENCES Electronic Industries, March 1946, pages 84-93, 126, 128, 130and 132.

